On Fri, Sep 2, 2016 at 12:15 PM, David Miller <[email protected]> wrote:
>
> The main thing I was concerned about was an I/O path that really
> expects the socket's hash not to change for whatever reason, but even
> all of the unix_find_other() calls are done outside of the mutex
> already.
That's my read of it too. I did actually go through the effort on
trying to follow all the locking in there yesterday, so while I would
want an AF_UNIX person to double-check me, I think it's fine.
The real locking seem to be the u->lock spinlock (taken by
unix_state_lock() and friends).
The bindlock is only about serializing the binders, which do things
that can sleep (notably the mknod of the unix socket node in the
filesystem).
The one thing I looked at and wasn't sure about was
unix_stream_connect(), which creates a *new* unix domain socket and
binds it to the old one without holding the bindlock. Note that it
never did hold the lock, so that's not a new thing, but it worries me
a bit.
I *think* it's ok, because I think this all happens before that new
socket is actually reachable, so it cannot race against somebody else
doing a bind. And my patch doesn't actually change anything in this
area, so I'm not making it worse. But it was the one thing I reacted
to when going through the locking there.
(Well, not the "one thing". The other thing I reacted to was the
overall reaction that none of this is documented, and the locking was
clearly not very clear).
Linus
